(1) Field of the Invention
The present invention relates to human prostatic epithelial and fibroblast cell lines which have been immortalized. In particular, the present invention relates to non-malignant cell lines immortalized with DNA of human papillomavirus (HPV) and malignant cell lines containing DNA of HPV and ras oncogene.
(2) Description of Related Art
Human cells are generally difficult to grow and maintain in long-term cultures in vitro. They have a limited life span in culture, grow for a short time and usually after 4 or 5 sub-cultures, they undergo senescence and die.
Prostate cancer is the leading cancer in men in the United States, in terms of incidence. Thirty-two percent (32%) of all cancers in men arise in the prostate. It is estimated by the American Cancer Society that 200,000 new cases of prostate cancer will occur in the U.S. in 1994. Prostate cancer is the second leading cause of death from cancer and 38,000 deaths are estimated to occur in 1994. African American men have the highest incidence of prostate cancer in the world, which is almost twice as high as that in white men and more than 600 times higher than in men from Thailand. One in 10 men in the U.S. by age 85 will develop prostate cancer in his lifetime. An estimated 11 million men have latent or clinical prostatic carcinoma. Approximately sixty-five (65%) of the cases already have metastatic disease at the time of diagnosis. The survival rate is less than 20% after metastasis.
The causes of prostate cancer are not known at the present time. A study of the causes, prevention and treatment has been hampered by the fact that no good animal or cell models are available. Although rat prostatic cells have been used extensively for such studies, rat prostate is not homologous to the human prostate, thus, it is not an ideal system to use.
There is a need for cell lines derived from normal human prostate which can be used for studies on the process of prostate cancer development in man and to identify agents which may cause or prevent prostate cancer.
Attempts have been made to immortalize human adult prostatic epithelial cells using a monkey virus (Simian virus SV40; Cussenot, O., et al., Journal of Urology 143, 881-886 (1991); Kaighn, M. E., et al, Cancer Research, 49, 3050-3056 (1989); Lee et al., Internat. J. Oncol. 4:821-830 (1994)). Only a monkey virus (SV40) fetal and adult human prostatic epithelial cells have been immortalized.
Human papillomavirus-18 (HPV-18) has been shown to immortalize human epithelial cells such as keratinocytes and cervical cells (Kaur, P., et al., Journal of Virology 62, 1917-1924 (1988); and Woodworth, C. D., et al., Cancer Research 48, 4620-4628 (1988)). The human papillomaviruses had never been used with human prostatic cells. An abstract was published in March 1993 describing an HPV immortalized prostatic epithelial cell line by the inventors and others; however, there was no disclosed method for producing the cells, particularly the use of a virus carrying a v-ki-ras oncogene for this purpose (Proceedings of the American Association for Cancer Research 34:117 (March 1993)).
There is increasing evidence for the involvement of the ras oncogenes and HPV infection in human prostatic carcinogenesis. Expression of activated ras oncogene has been demonstrated in human prostate adenocarcinomas (Viola et al., N. England J. Med. 314:133-137 (1986)). Additionally, a relatively high frequency (27%) of Ki-ras codon 12 mutation in human prostate carcinomas has also been detected by PCR amplification (Carter, B. S., et al., Cancer Research 50, 6830-6832 (1990)). In separate studies, a high prevalence of high-risk HPV DNA in human prostate carcinomas has been described (McNicol, J. P., et al., Journal of Urology 145, 850-853 (1991)). PCR analysis of type-specific HPV-sequences has been used to assess the prevalence of HPV DNA in prostate tissues from 83 Canadian patients. HPV DNA was found in 35 of 56 benign prostatic hyperplasia and in 14 of 27 prostate carcinomas. At least in one study, development of disease correlated with both the presence of HPV sequences and the activation of cellular ras genes (Anwar, K., et al., Cancer Research 52, 5991-5996 (1992)). Anwar et al. examined the frequency of ras mutations and the presence of high-risk HPV DNA sequences in 75 specimens from Japanese patients with prostate carcinomas using PCR amplification (Anwar, K., et al., Cancer Research 52, 5991-5996 (1992)). Mutant ras genes were present in 41% of cases and the frequency of ras mutations and HPV infection increased in patients with advanced tumors.